Through wafer vias and method of making same

ABSTRACT

A method of forming and structure for through wafer vias and signal transmission lines formed of through wafer vias. The structure includes, a semiconductor substrate having a top surface and an opposite bottom surface; and an array of through wafer vias comprising at least one electrically conductive through wafer via and at least one electrically non-conductive through wafer via, each through wafer via of the array of through wafer vias extending from the top surface of to the bottom surface of the substrate, the at least one electrically conductive via electrically isolated from the substrate.

RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.12/188,241 filed on Aug. 8, 2008 now U.S. Pat. No. 8,384,224, issuedFeb. 26, 2013.

FIELD OF THE INVENTION

The present invention relates to the field of integrated circuit chips;more specifically, it relates to through wafer vias for use inintegrated circuit chips and the method of fabricating the through wafervias.

BACKGROUND OF THE INVENTION

To increase the density of devices using integrated circuit chips it isdesirable to allow interconnections to be made to both the top andbottom surfaces of the integrated circuit chip. This requires formationof through wafer vias from the top to the bottom surface of theintegrated chip that are compatible with carrying both high frequencyand DC signals. Many existing through via schemes are either difficultto integrate into existing integrated circuit fabrication processes orresult in unacceptable degradation of signals propagating from/to thefront surface of the integrated circuit chip to/from the bottom surfaceof the integrated circuit chip. Accordingly, there exists a need in theart to overcome the deficiencies and limitations described hereinabove.

SUMMARY OF THE INVENTION

A first aspect of the present invention is a structure, comprising: asemiconductor substrate having a top surface and an opposite bottomsurface; and an array of through wafer vias comprising at least oneelectrically conductive through wafer via and at least one electricallynon-conductive through wafer via, each through wafer via of the array ofthrough wafer vias extending from the top surface of to the bottomsurface of the substrate, the at least one electrically conductive viaelectrically isolated from the substrate.

A second aspect of the present invention is a method, comprising:forming an array of through wafer vias comprising at least oneelectrically conductive through wafer via and at least one electricallynon-conductive through wafer via, through a semiconductor substratehaving a top surface and an opposite bottom surface, each through wafervia of the array of through wafer vias extending from the top surface ofto the bottom surface of the substrate, the at least one electricallyconductive via electrically isolated from the substrate.

A third aspect of the present invention is a method, comprising: (a)forming a first trench and a second trench in a semiconductor substrate,the first and second trenches extending in a first direction from a topsurface of the substrate toward an opposite bottom surface of thesubstrate a distance less than a thickness of the substrate in the firstdirection; after (a), (b) simultaneously forming a first liner of adielectric material on sidewalls of the first trench and a second linerof the dielectric material on sidewalls of the second trench; after (b),(c) filling remaining space in the first trench with an electricallyconductive material and forming a third liner of the electricallyconductive material on the second liner, the third liner not completelyfilling the second trench; after (c), (d), filling remaining space inthe second trench with a polysilicon core, recessing the polysiliconcore and the third liner below the top surface of the substrate, andforming, in the second trench, a dielectric plug on the polysilicon coreand the third liner; and after (d), (e) thinning the substrate from thebottom surface of the substrate to form a new bottom surface of thesubstrate, the electrically conductive material of the first trench andthe liner and polysilicon core of the second trench exposed in the newbottom surface of substrate.

A fourth aspect of the present invention is a signal transmission linethrough a semiconductor substrate, the substrate having a top surfaceand an opposite bottom surface, comprising: a conductive through viaextending from the top surface of the substrate to the bottom surface ofthe substrate, sidewalls of the conductive through via in physical andelectrical contact with the substrate, sidewalls of the conductivethrough via electrically insulated from the substrate; and anon-conductive through via extending from the top surface of thesubstrate to the bottom surface of the substrate, the nonconductivethrough via proximate to and separated from the conductive through wafervia by a region of the substrate, the non-conductive through viacomprising a conductive core electrically insulated from the substrateby a dielectric liner and having a dielectric plug recessed between theliner in an end proximate to the top surface of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention are set forth in the appended claims. Theinvention itself, however, will be best understood by reference to thefollowing detailed description of an illustrative embodiment when readin conjunction with the accompanying drawings, wherein:

FIGS. 1A through 1K are cross-sectional drawings illustrating initialsteps in the fabrication of an array of through wafer vias accordingembodiments of the present invention;

FIGS. 2A through 2J are cross-sectional drawings illustrating completionof the fabrication of the array of through wafer vias according toembodiments of the present invention and fabrication of athree-dimensional device using arrays of through wafer vias according toembodiments of the present inventions;

FIGS. 3A through 3D are plan views of through wafer vias according toembodiments of the present inventions;

FIGS. 4A through 4D are schematic plan views of waveguide models usingthrough wafer vias according to embodiments of the present invention;

FIG. 5 is cross-sectional drawing illustrating an alternative throughwafer via structure according to embodiments of the present invention;

FIG. 6A illustrates the phenomena of wide trenches etching deeper thannarrow trenches and FIG. 6B and FIG. 6B illustrates a method ofmitigating the effect of wide trenches etching deeper than narrowtrenches; and

FIGS. 7A through 7D illustrate an alternative method of fabricatingthrough vias according to embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The term through wafer via defines a structure that extends from a topsurface of a substrate, through the substrate, to an opposite bottomsurface of the substrate of the packaged integrated circuit or chip. Athrough wafer via according to the embodiments of the present inventionmay be electrically conductive or electrically non-conductive. Althoughin the description infra, both conductive and non-conductive (i.e.,insulating) through vias are described and illustrated as extending fromthe top to the bottom surface of the chip, the present invention may bepracticed where the conductive through via extends entirely through thechip, but the non-conductive only extends partially through the chipbecause one purpose of the non-conductive through vias is for isolationand not passing electrical signals between the top and bottom surfacesof the chip. An electrically conductive through via includes at leastone electrically conductive element and may include non-electricallyconductive elements. An electrically non-conductive through via includesat least one electrically non-conductive element and may includeelectrically conductive elements that are surrounded completely byelectrically non-conductive elements. The “wafer” of through wafer viaderives from the fact that the via is formed before integrated circuitshave been singulated from a semiconductor substrate called a wafer. Theterm “ three dimensional device” defines a device comprising two or moreindividual substrates electrically connected and in physical contact bybeing stacked one upon another.

FIGS. 1A through 1K are cross-sectional drawings illustratingfabrication of a through wafer via is according an embodiment of thepresent invention. In FIG. 1A, a semiconductor substrate 100 has a topsurface 105. Formed on top surface 105 is a first dielectric layer 110.Formed on a top surface 115 of first dielectric layer 110 is a seconddielectric layer 120. First and second dielectric layers 110 and 120 areexemplary and there may be a few as one dielectric layer or more thantwo dielectric layers formed over top surface 105 of substrate 100. Inone example, substrate 100 comprise silicon. In one example firstdielectric layer 110 is silicon dioxide and second dielectric layer 120is silicon nitride.

In FIG. 1B, trenches 125 and 130 are etched through first and seconddielectric layers 110 and 120 and into substrate 100. Trenches 125 and130 may be formed using a photolithographic/etching process. Anexemplary photolithographic/etching process comprises (1) forming aphotoresist layer on second dielectric layer 120, (2) forming openingsin the photoresist layer by exposing the photoresist layer to actinicradiation through a patterned photomask and developing away either theexposed or unexposed regions of the photoresist, (4) etching through,the first and second dielectric layers using, for example, a reactiveion etch (RIE) process, (5) removing the patterned photoresist layer,and (6) etching substrate 100 using, for example, an RIE process usingthe pattern in the first and second dielectric layers as a patternedhardmask. Although trenches 125 and 130 are shown etched to the samedepth in FIG. 1B, trenches 125 and 130 may be etched to differentdepths. For example, an etch process commonly referred to as the “Bosch”silicon etch process will etch trenches having wide (W2) openings deeperthen trenches having narrow openings (W1). This phenomena illustrated inFIG. 6A. If the etch depth differences are small, this effect presentsno problem as the thinning processes described infra can be adjusted toover-thin to compensate. Otherwise the alternative processes illustratedin FIGS. 6A and 7A-7D and described infra can be performed.

Trenches 125 and 130 extend into substrate 100 a distance D1 from topsurface 105 of the substrate. Trenches 125 have a width W1 and trench130 has a width W2. W2 is greater than W1. In one example, W1 is about 1micron to about 3 microns. In one example, W2 is about 3 microns toabout 10 microns. In one example D1 is about 50 microns to about 200microns. In one example W1 is about 2 microns, W2 is about 5 microns andD1 is about 150 microns. Since trenches 125 and 130 may be elongated inand out of the plane of the drawings (i.e., are rectangles when viewedfrom above), W1 and W2 measure minimum widths of trenches 125 and 130(i. e., the short side of the rectangle).

In FIG. 1C, a polysilicon layer 135 is deposited on top surfaces 140 ofsecond dielectric layer 120, sidewalls 145 and bottoms 150 of trenches125 and 130. In one example, polysilicon layer 135 comprises an N or aP-type doped polysilicon. In one example, polysilicon layer 135comprises boron doped polysilicon. Polysilicon layer 135 has a thicknessT1. In one example, T1 is about 0.8 microns to about 2.4 microns.

In FIG. 1D an oxidation is performed to convert polysilicon layer 135(see FIG. 1C) to a silicon dioxide layer 155. Silicon dioxide layer 155has a thickness T2. Silicon dioxide layer 155 does not completely filltrenches 125 and 130, because the width of trenches 125 and 130 (W1 andW2 respectively in FIG. 1B) are both less than twice the thickness T2 ofsilicon dioxide layer 155. In one example, the oxidation of polysiliconlayer 135 (see FIG. 1C) to form silicon dioxide layer 155 is performedusing a high pressure oxidation (HIPOX) process. In one example, T2 isabout equal to or less than a quarter of W1. After oxidation, thedistance between opposite sides of silicon dioxide layer 155 on thesidewalls of trenches 130 is W3 and the distance between opposite sidesof silicon dioxide layer 155 on the sidewalls of trench 125 is W4, withW3 greater than W4.

HIPOX of boron doped polysilicon (i.e., layer 135 of FIG. 1C) ispreferred because of the high oxidation rate of born doped polysiliconand the ability of HIPOX to form uniform oxide thicknesses in deeptrenches.

Alternatively, the structure illustrated in FIG. 1D may be formed byoxidation (e.g., in a furnace) of the sidewalls and bottoms of trenches125 and 130 of FIG. 2B or by deposition (e.g., by chemical vapordeposition (CVD) or atomic layer deposition (ALD)) of oxide on thesidewalls and bottom of trenches 125 and 130.

In FIG. 1E, a conformal and electrically conductive layer 160 is formed(for example, by evaporation and/or sputtering) over all exposedsurfaces of silicon dioxide layer 155. Electrically conductive layer 160completely fills trenches 125 but does not completely fill trench 130.

In one example, electrically conductive layer 160 comprises a metal. Inone example, electrically conductive layer 160 comprises tungsten (W) ortungsten and titanium nitride (TiN). In one example, electricallyconductive layer 160 comprises a first deposited conformal layer oftitanium nitride and a second deposited layer of tungsten. In oneexample, electrically conductive layer 160 comprises a first depositedconformal layer of titanium nitride, a second deposited layer ofconformal titanium (Ti) and a third deposited layer of tungsten.Titanium, titanium nitride and tungsten may be deposited using CVD.

In one example, electrically conductive layer 160 comprises tungsten ortungsten and tantalum nitride (TaN). In one example, electricallyconductive layer 160 comprises a first deposited conformal layer oftantalum nitride and a second deposited layer of tungsten. In oneexample, electrically conductive layer 160 comprises a first depositedconformal layer of tantalum nitride, a second deposited layer ofconformal tantalum (Ta) and a third deposited layer of tungsten.Tantalum and tantalum nitride and may be deposited using CVD.

Other metallurgical combinations that may be used for electricallyconductive layer 160 include combinations of copper (Cu), ruthenium(Ru), Ta and TaN. Those combinations include the following combinations,each of which is in the order of formation: Ta/Cu, TaN/Cu, Ru/Cu,TaN/Ta/Cu/, TaN/Ru/Cu, Ta/Ru/Cu, Ru/Ta/Cu, Ru/TaN/Cu, TaN/Ta/Ru/Cu.

Electrically conductive layer 160 has a thickness T3, where T3 is equalto greater than half of W4, but less than half of W3 (see FIG. 1D).

In FIG. 1F, a polysilicon layer 170 is formed all exposed surface ofelectrically conductive layer 160. Polysilicon layer 170 completelyfills the remaining space in trench 130. In one example, polysiliconlayer 170 comprises intrinsic (i.e., undoped) polysilicon.

In FIG. 2G, electrically conductive layer 160 is removed from overtrench 130 and recessed along with polysilicon layer 170 below topsurface 105 of substrate 100. The polysilicon recess process removes allof polysilicon layer 170 not in trench 130 and from an upper region oftrench 130. A surface 172 of polysilicon layer 170 remaining in trench130 after the recess process and edges 162 of electrically conductivelayer 160 are below top surface 105 of substrate 100. The layer 160removal process and polysilicon recess process may be independentlyperformed using RIEs, wet etches, or combinations of RIEs and wetetches. In the preferred embodiment, this recess extends belowdielectric layer 110, to facilitate the capping of the trench with layer180, as shown in FIGS. 1H and I1.

In FIG. 1H, a dielectric layer 180 is formed on top surface 175 ofelectrically conductive layer 160 and completely fills the upper regionof trench 130 above polysilicon layer 170. In one example dielectriclayer 180 comprises TEOS oxide (oxide formed by CVD usingtetraethoxysilane precursor).

In FIG. 1I, using a chemical-mechanical-polish (CMP) process, dielectriclayer 180, electrically conductive layer 160, silicon dioxide layer 155,second dielectric layer 120 and first dielectric layer 110 (see FIG. 2H)are removed above top surface 105 of substrate 100 and a new firstdielectric layer 190 and a new second dielectric layer 195 are formed onnew top surface 105A of substrate 100. Silicon dioxide layer 155,electrically conductive layer 160 and polysilicon layer 170 remain intrench 130, electrically conductive layer 160 and polysilicon layer 170are capped by dielectric layer 180 in trench 130. The respective fillmaterials in trenches 125 and 130 are protected by a protective layercomprising first and second dielectric layers 190 and 195. In oneexample first dielectric layer 190 is silicon dioxide and seconddielectric layer 195 is silicon nitride.

In FIG. 1J, first, STI 200 has been formed in substrate 100 by aphotolithographic/etching process in combination new first and seconddielectric layers 190 and 195 (see FIG. 1J) similar to that describedsupra followed by a TEOS CVD followed by a CMP. Second, additionalphotolithographic/etching process/deposition process have been performedto form a FET 205 and a trench capacitor 210. FET 205 and trenchcapacitor are examples of integrated circuit devices that may be formedat this point in fabrication. Other devices that may be formed at thispoint include bipolar transistors, BiCMOS SiGe transistors, diodes andresistors. FET 205 includes source/drains 215, a gate dielectric 220, agate electrode 225, and silicide contacts 230. Trench capacitor 210includes an inner plate 235 and a dielectric layer 238. Third, new firstand second dielectric layers 190 and 195 are removed and a firstinterlevel dielectric layer 240 is formed over a new top surface 105B ofsubstrate 100. Interlevel dielectric layer 240, by way of example,comprises a lower dielectric layer 245 and an upper dielectric layer250. Interlevel dielectric layer 240 may be a single layer or mayinclude more than two layers. In one example, lower dielectric layer 245comprises silicon nitride and upper dielectric layer 250boro-phosphosilicate glass (BPSG).

In FIG. 1J and subsequent FIG. 1K, lower dielectric layer 245 is shownas not covering gate 225 of FET 205 for clarity. In actuality, lowerdielectric layer 245 may cover gate 225 of FET 205.

In FIG. 1K, a stud contact 265 to source/drain 230 of FET 205 and studcontacts 280 to electrically conductive layers 160 in trenches 125 aresimultaneously formed in lower and upper dielectric layers 245 and 250.Stud contacts 265 and 280 may be formed, for example, by (1) aphotolithographic/etching process as described supra to define openingsin lower and upper dielectric layers 245 and 250, (2) removing thephotoresist, (3) evaporating, sputtering or depositing a conductivematerial of sufficient thickness to fill the openings and (4) performinga CMP to remove excess conductive material and expose a top surface ofupper dielectric layer 250. Top surfaces of stud contacts 265 and 280are coplanar with a top surface of upper dielectric layer 250. In oneexample, stud contacts 265 and 280 comprise a metal.

In one example, stud contacts 265 and 280 comprise tungsten (W) ortungsten and titanium nitride (TiN). In one example, stud contacts 265and 280 comprise a first deposited conformal layer of titanium nitrideand a second deposited layer of tungsten. In one example, stud contacts265 and 280 comprise a first deposited conformal layer of titaniumnitride, a second deposited layer of conformal titanium (Ti) and a thirddeposited layer of tungsten. Titanium, titanium nitride and tungsten maybe deposited using CVD.

In one example, stud contacts 265 and 280 comprise tungsten or tungstenand tantalum nitride (TaN). In one example, stud contacts 265 and 280comprise a first deposited conformal layer of tantalum nitride and asecond deposited layer of tungsten. In one example, stud contacts 265and 280 comprise a first deposited conformal layer of tantalum nitride,a second deposited layer of conformal tantalum (Ta) and a thirddeposited layer of tungsten. Tantalum and tantalum nitride and may bedeposited using CVD.

Other metallurgical combinations that may be used for stud contacts 265and 280 include combinations of copper (Cu), ruthenium (Ru), Ta and TaN.Those combinations include the following combinations, each of which isin the order of formation: Ta/Cu, TaN/Cu, Ru/Cu, TaN/Ta/Cu/, TaN/Ru/Cu,Ta/Ru/Cu, Ru/Ta/Cu, Ru/TaN/Cu, TaN/Ta/Ru/Cu.

It should be understood, that many other stud contacts 265 are formed atthis time to other devices in substrate 100. It should be understood,that many other stud contacts 265 are formed at this time to otherdevices in substrate 100. It should be also understood that by thinningsubstrate 100 from the bottom a through wafer via will be formed asillustrated in FIGS. 4A through 4J and described infra. Electricallyconductive layers 160 in trenches 125 and 130 are electrically isolatedfrom substrate 100 by silicon dioxide layer 155.

FIGS. 2A through 2J are cross-sectional drawings illustrating completionof the fabrication of the array of through wafer vias according toembodiments of the present invention and fabrication of athree-dimensional device using arrays of through wafer vias according toembodiments of the present inventions. In FIGS. 2A through 2J, the depthof the narrow trenches are illustrated as being the same. As mentionedsupra, there are processes that may be applied if the widths if the wideand narrow trenches are such as to result in significant differences inetch depth. These alternative processes illustrated in FIGS. 6A and7A-7D and described infra.

In FIG. 2A, (not drawn to scale) formed in a set of interleveldielectric layers 300 are corresponding wires and vias 305. An optionalterminal pad 310 is formed on a top surface 315 of the set of interleveldielectric layers 300 and is in electrical contact with an uppermostwire 305 in an uppermost interlevel dielectric layer of the set ofinterlevel dielectric layers 300. Wires in a lowermost interleveldielectric layer of the set of interlevel dielectric layers are inphysical and electrical contact with stud contacts 265 and 280.Individual interlevel dielectric layers of the set of interleveldielectric layers 300 are not illustrated in FIG. 2A. A handle substrate325 is attached to top surface 315 of the set of interlevel dielectriclayers 300. Handle wafer 325 is attached using a layer of adhesive (notshown). In one example, handle substrate 325 is a quartz wafer.

In FIG. 2B, substrate 100 is thinned from the bottom (for example, bygrinding) to form a new bottom surface 320 that is a distance D2 fromtrenches 125 and 130. In one example, D2 is about 5 microns to about 50microns. In one example, D2 is about 20 microns. After thinning, thethickness of substrate 100 is D3. In one example, D3 is about 50 micronsto about 200 microns. In one example, D3 is about 170 microns.

In FIG. 2C, a RIE or wet etch selective to silicon is preformed torecess bottom surface 320 (see FIG. 1B) of substrate 100 so the fillmaterial of trenches 125 and 130 protrudes above a new top surface 320A.

In FIG. 2D, a CMP is performed to remove the fill material protrudingabove top surface 320A (see FIG. 2C) to form through wafer via arrays330. In the example of FIG. 2D, each through wafer via array 330includes two conductive through wafer vias 125A and one non-conductivethrough via 130A. While the core formed of polysilicon layer 170 andliner formed of electrically conductive material 160 of through wafervia 130A is conductive, because of the plug formed of dielectric layer180 (see FIG. 1I) through wafer via 130A is defined as a non-conductivethrough wafer via relative to conducting electricity from front surface105 to bottom surface 335. After the CMP, the electrically conductivelayer 160, polysilicon layer 160 and silicon dioxide layers 155 (seeFIG. 1K) of through wafer vias 125A and 130A are exposed at bottomsurface 320 of substrate 100.

In FIG. 2E, a RIE or wet etch selective to preferentially etch siliconover silicon dioxide is preformed to recess bottom surface 320A (seeFIG. 2D) below the bottoms of through wafer via arrays 330 and to form anew bottom surface 335 of substrate 100.

In FIG. 2F, a dielectric layer 340 is formed over bottom surface 335 ofsubstrate and over through wafer via arrays 330. In one example,dielectric layer 340 is a plasma enhanced chemical vapor deposition(PECVD) silicon oxide.

In FIG. 2G, a CMP is performed to remove dielectric layer 340 from overthe bottom surfaces of through wafer via arrays 330. Dielectric layer340 remains on bottom surface 335 of dielectric layer 340 and dielectriclayer 340 fills any spaces between through wafer via arrays 330 betweenindividual through wafer vias 125A and 130A of each of the through wafervia arrays. Bottom surfaces of through wafer vias 125A and 130A arecoplanar with a top surface 350 of dielectric layer 340.

Alternatively, the backside grind process illustrated in FIG. 2B anddescribed supra, can be continued until non-conductive through wafervias 125A and conductive through wafer vias 130A of FIG. 2D are formeddirectly (skipping the processes of FIG. 2C) or after grinding and a“clean-up” CMP to remove any grinding damage to the through wafer viasand surface 320A (see FIG. 2D).

It should be noted that through wafer via 125A is a trench having afilling consisting only of a dielectric liner surrounding anelectrically conductive core and through wafer via 130A is a trenchfilled only a dielectric liner surrounding an electrically conductiveliner which in turn surrounds a polysilicon core with a dielectric plugbetween the dielectric liner and over the conductive liner andpolysilicon core at one end.

In FIG. 2H, electrically conductive pads 345 are formed on top surface350 of dielectric layer 340 on through wafer via arrays 330 andelectrically conductive solder bumps 355 are formed on pads 345. In oneexample, pads 345 and solder bumps 355 are formed by electroplatingthrough a patterned photoresist layer or by evaporation through a metalmask. If pads 345 are formed by plating, a thin electrically seed layeris first deposited, which is removed after the photoresist layer isremoved, by RIE or wet etching.

In FIG. 2I, handle wafer 325 (see FIG. 2G) is removed, either prior toor after chip dicing. An exemplary method of removing handle wafer 325is to expose the adhesive to ultraviolet radiation as is well known inthe art. In a preferred embodiment, handle wafer 325 is removed afterdicing to minimize the potential for breaking the thinned wafer.

FIG. 2J is an exploded view prior to a solder reflow step. In FIG. 2J,an upper substrate 360 containing electrical components is aligned toterminal pad 310 by electrically conductive solder bumps 365, andsubstrate 100 is aligned to a lower substrate 370 having electricallyconductive pads 375 and containing electrical components (not shown) bysolder bumps 355. This arrangement allows for self alignment of thethree components prior to the anneal which melts the solder bumps,electrically wires substrates 100, 360 and 370 together and completesthe fabrication process. Examples of electrical components include butare not limited to, transistors, diodes, resistors, capacitors,inductors and wires.

While pad to solder bump connections are illustrated in FIG. 2J, otherconnection types such as pad to pad may be used (i) between substrate360 and substrate 100, (ii) between substrate 100 and substrate 370 or(iii) between substrate 360 and substrate 100 and between substrate 100and substrate 370 substrate. While solder bumps are shown on substrate360 and pads on substrate 100, pads may be formed on substrate 360 andsolder bumps on substrate 370. While the solder bumps are shown onsubstrate 100 and pads on substrate 370, pads may be formed on substrate100 and solder bumps on substrate 370. Substrate 360 may be replacedwith wire or tab bonds. If the solder bumps and pads of substrate 100are swapped, then substrate 370 may be replaced with wire or tab bonds.

FIGS. 3A through 3D are exemplary plan views of through wafer viasaccording to embodiments of the present inventions. In FIG. 3A, a singlethrough wafer via array 330A consists of an electrically conductivethrough wafer via 125A consisting of a electrically conductive core ofelectrically conductive material 160 surrounded by a liner of silicondioxide layer 155 and a single electrically non-conductive through wafervia 130A comprising an electrically conductive liner of electricallyconductive material 160 intervening between a dielectric liner ofsilicon dioxide layer 155 and a core of polysilicon layer 170 and adielectric plug of dielectric layer 180 (not illustrated in FIG. 3A (orFIGS. 3B, 3C and 3D, see FIG. 1K)).

In FIG. 3B, a through wafer via array 330B consists of two electricallynon-conductive through wafer vias 130A on opposite sides of electricallynon-conductive through wafer via 125A.

In FIG. 3C, a through wafer via 330C consists of four electricallynon-conductive through wafer vias 130A on opposite each of the foursides of electrically conductive through wafer via 125A.

In FIG. 3D, through wafer via 330D consists of seven electricallynon-conductive through wafer vias 130A and two electrically conductivethrough wafer vias 125. Three of the electrically non-conductive throughwafer vias 130A are positioned between the two electrically conductivethrough wafer vias 125A. Four of the electrically non-conductive throughwafer vias 125A are positioned opposite each of the four sides formed bythe combination the first three non-electrically conductive throughwafer vias 130A and the two through electrically conductive throughwafer vias 125A. Through wafer vias 330B, 330C and 330D function ascoplanar waveguides.

In each of FIGS. 3A, 3B, 3C and 3D every through wafer via 125A and 130Ais surrounded by a region of substrate 100. Through wafer vias 330B,330C and 330D function as coplanar waveguides.

Through wafers vias of the present embodiment of the present inventionincludes at least one electrically conductive element extending from thetop surface of the substrate, through the substrate, to the bottomsurface of the substrate and at least one non-electrically conductive(i.e., dielectric or insulator) element also extending from the topsurface of the substrate, through the substrate, to the bottom surfaceof the substrate.

It should be understood that very many other through wafer via arrayshaving different numbers and configurations of through wafers vias 125Aand 130A are possible and are not limited to those illustrated in FIGS.3A, 3B, 3C and 3D.

FIGS. 4A through 4D are schematic plan views of waveguide models usingthrough wafer vias according to embodiments of the present invention. InFIGS. 4A, 4B, 4C and 4D, G indicates an electrical conductor filledtrench that is not insulated from the substrate and that is connected toground, S indicates an electrical conductor filled trench that is notinsulated from the substrate and is connected to a signal source, Iindicates an electrical insulator filled trench, IG indicates anelectrical conductor filled trench connected to ground and that isinsulated from the substrate and IS indicates an electrical conductorfilled trench connected to a signal source and that is insulated fromthe substrate. The space between the G, S, I, IG and IS structures issubstrate.

The structures of FIGS. 4A, 4B, 4C and 4D were modeled as signalwaveguides for characteristic impedance, propagation loss and effectivedielectric constant (Er). Low propagation loss and small effectivedielectric constant are preferred. The model was based on a siliconsubstrate with a relative dielectric constant of 11.9 and a conductivityof 7.41 Siemens/meter; tungsten with a conductivity of 1.82E7Siemens/meter for the electrical conductor for the G, IG, S and ISstructures; and silicon dioxide with a relative dielectric constant of4.1 for the insulator of the I, IG and IS structures.

The dimensions of the G and S structures in top view was 50 by 3microns. The dimensions of the IG and IS structures in top view was 52by 5 microns (the G and S structures with a surrounding insulator 1micron thick). The dimensions of the I structures in top view was 52 by5 microns. Simulation was performed on an Ansoft HFSS-3D full wave EMsimulator. Table I gives the result of the simulation for each of thestructures of FIGS. 4A, 4B 4C and 4D.

TABLE I Propagation Characteristic Propagation Loss Loss CASE Impedance(dB/mm) % of Case 1 Effective Er FIG. 4A 22.61 + j0.96 1.329 100 12.136FIG. 4B 24.08 + j071 1.062 79.9 10.722 FIG. 4C 27.07 + j0.37 0.777 58.58.4657 FIG. 4D 28.42 + j0.23 0.635 47.8 7.7056

The following conclusions can be reached as a result of the simulation.For coplanar waveguides, insulated through wafer vias have a highercharacteristic impedance, less propagation loss, lower effectivedielectric constant and is better for signal propagation with lesspotential un-wanted coupling. The reasons are, silicon is lossy, butsilicon dioxide is not. The higher dielectric constant of silicon causeshigher parasitic capacitance relative to parasitic capacitance of thelower dielectric constant silicon dioxide.

Thus, a through wafer via that contacts the substrate directly (Gstructure) as in the embodiments of the present invention, may be usedfor the ground structure as long as the voltage across the through wafervia is low enough for little or no current is conducted through thesubstrate. For the signal structure, an insulated conductor (ISstructure) such as in the second and third embodiments of the presentinvention is preferred to reduce signal conduction through thesubstrate.

FIG. 5 is cross-sectional drawing illustrating an alternative throughwafer via structure according to the embodiments of the presentinvention. When polysilicon is deposited into a deep trench, there is atendency for a void to be formed where the polysilicon deposited onopposite sidewalls meet in what is called the seam. The void formsbecause of pinch-off at the top of the trench. This can result in aslightly different structure than that shown in FIG. 1K. FIG. 5 issimilar to FIG. 1K except dielectric layer 180 extends into a void 350in polysilicon layer 170.

FIG. 6A illustrates the phenomena of wide trenches (130B) etching deeperthan narrow trenches (125). FIG. 6A is a cross-sectional drawingillustrating an alternative structure to that illustrated in FIG. 1B. InFIG. 5, trench 130B extend a distance D3 into substrate 100 from topsurface 105, while trenches 125 extend into substrate 100 from topsurface 105 the distance D2 as described supra with respect to FIG. 1B.D3 is greater than D2, while D2 is equal to D1 (see FIG. 1B).

FIG. 6B illustrates a method of mitigating the effect of wide trenchesetching deeper than narrow trenches. In FIG. 6B, a buried oxide layer102 has been formed a distance D2 into substrate 100. Trenches 125 and130B will stop etching vertically when buried oxide layer 102 isreached. In one example substrate 100 is a silicon-on-insulatorsubstrate and buried oxide layer 102 is silicon oxide.

FIGS. 7A through 7D illustrate an alternative method of fabricatingthrough vias according to embodiments of the present invention. FIG. 7Ais similar to 1H except trenches 125 and 130 were the same width soafter the processing described supra with respect to FIGS. 1A through 1Gare preformed, the fill of trenches 125 is the same as for trench 130.In FIG. 7B openings over trenches 125 are made in layer 185. In FIG. 7Bplug 185, polysilicon are removed in trenches 125. FIG. 7D is similar toFIG. 1M after the steps described in reference to FIGS. 1L and 1M havebeen performed.

Thus, the embodiments of the present invention provide a structure andmethod to integrate through wafer vias into existing integrated circuitfabrication processes having in good propagation of signals from/to thefront surface of the integrated circuit chip to/from the bottom surfaceof the integrated circuit chip.

The description of the embodiments of the present invention is givenabove for the understanding of the present invention. It will beunderstood that the invention is not limited to the particularembodiments described herein, but is capable of various modifications,rearrangements and substitutions as will now become apparent to thoseskilled in the art without departing from the scope of the invention.Therefore, it is intended that the following claims cover all suchmodifications and changes as fall within the true spirit and scope ofthe invention.

What is claimed is:
 1. A method, comprising: (a) forming a first trenchand a second trench in a semiconductor substrate, said first and secondtrenches extending in a first direction from a top surface of saidsubstrate toward an opposite bottom surface of said substrate a distanceless than a thickness of said substrate in said first direction; after(a), (b) simultaneously forming a first liner of a dielectric materialon sidewalls of said first trench and a second liner of said dielectricmaterial on sidewalls of said second trench; after (b), (c) fillingremaining space in said first trench with an electrically conductivematerial and forming a third liner of said electrically conductivematerial on said second liner, said third liner not completely fillingsaid second trench; after (c), (d), filling remaining space in saidsecond trench with a polysilicon core, recessing said polysilicon coreand said third liner below said top surface of said substrate, andforming, in said second trench, a dielectric plug on said polysiliconcore and said third liner; and after (d), (e) thinning said substratefrom said bottom surface of said substrate to form a new bottom surfaceof said substrate, said electrically conductive material of said firsttrench and said liner and polysilicon core of said second trench exposedin said new bottom surface of substrate.
 2. The method of claim 1,wherein (b) includes: forming a polysilicon layer on sidewalls of saidfirst trench and on said sidewalls of said second trench; and oxidizingsaid polysilicon layer to form said first liner on sidewalls of saidfirst trench and said second liner on sidewalls of said second trench.3. The method of claim 2, wherein said polysilicon is doped with boron.4. The method of claim 1, wherein (e) includes: grinding said bottomsurface of said substrate to form a ground surface of said substrate;chemically etching said ground surface of said substrate to expose saidelectrically conductive material of said first trench and said liner ofsaid second trench; and chemical-mechanical-polishing said conductivematerial of said first trench and said liner and polysilicon core ofsaid second trench.
 5. The method of claim 1, further including: formingan electrically conductive backside pad in physical and electricalcontact with said electrically conductive material of said first trench,said dielectric liner of said second trench and said polysilicon core ofsaid second trench.
 6. The method of claim 5, further including: (f)forming an insulating layer on said new bottom surface of saidsubstrate, said electrically conductive material of said first trenchextending through said insulating layer and said dielectric liner andpolysilicon core of said second trench extending through said insulatinglayer, said backside pad formed on said insulating layer.
 7. The methodof claim 1, wherein said electrically conductive material comprises (i)tungsten, (ii) copper, (iii) tungsten in combination with titanium,titanium nitride or titanium and titanium nitride, (iv) tungsten incombination with tantalum and tantalum nitride, (v) copper incombination with one or more of titanium, titanium nitride andruthenium, or (vi) copper in combination with one or more of tantalum,tantalum nitride and ruthenium.
 8. A method of forming signaltransmission line through a semiconductor substrate, said substratehaving a top surface and an opposite bottom surface, comprising: forminga conductive through via extending from said top surface of saidsubstrate to said bottom surface of said substrate, sidewalls of saidconductive through via in physical and electrical contact with saidsubstrate, sidewalls of said conductive through via electricallyinsulated from said substrate; and forming a non-conductive through viaextending from said top surface of said substrate to said bottom surfaceof said substrate, said nonconductive through via proximate to andseparated from said conductive through wafer via by a region of saidsubstrate, said non-conductive through via comprising a conductive coreelectrically insulated from said substrate by a dielectric liner andhaving a dielectric plug recessed between said liner in an end proximateto said top surface of said substrate.
 9. The method of claim 8, furtherincluding; forming an additional non-conductive through via extendingfrom said top surface of said substrate to said bottom surface of saidsubstrate, said additional non-conductive through via disposed on anopposite side of said conductive through via from said non-conductivethrough via, said additional nonconductive through via proximate to andseparated from said conductive through via by an additional region ofsaid substrate, said additional non-conductive through via comprising aconductive core electrically insulated from said substrate by adielectric liner and having a dielectric plug recessed between saidliner in an end proximate to said top surface of said substrate.
 10. Themethod of claim 8, further including: forming first, second and thirdadditional non-conductive through vias extending from said top surfaceof said substrate to said bottom surface of said substrate, saidnon-conductive through via and said first, second and third additionalnon-conductive through vias disposed on respective first, second, thirdand fourth sides of said conductive through via, said first sideopposite said second side, said third side opposite said fourth side;said first, second and third additional non-conductive through viasseparated from said conductive through region by respective first,second and third additional regions of said substrate, said first,second and third additional non-conductive through vias each comprisinga conductive core electrically insulated from said substrate by adielectric liner and having a dielectric plug recessed between saidliner in an end proximate to said top surface of said substrate.
 11. Themethod of claim 8, further including: forming an additional conductivethrough via extending from said top surface of said substrate to saidbottom surface of said substrate, sidewalls of said additionalconductive through via in physical and electrical contact with saidsubstrate, sidewalls of said additional conductive through viaelectrically insulated from said substrate.
 12. The method of claim 11,further including: forming one or more interior non-conductive throughvias extending from said top surface to said bottom surface of saidsubstrate, said one or more interior non-conductive through viasintervening between said conductive through via and said additionalconductive through via, said one or more interior non-conductive throughvias on an opposite side of said conductive through via from saidnon-conductive through via, said one or more interior non-conductivethrough vias each comprising a conductive core electrically insulatedfrom said substrate by a dielectric liner and having a dielectric plugrecessed between said liner in an end proximate to said top surface ofsaid substrate.
 13. The method of claim 12, further including: anadditional non-conductive through via extending from said top surface ofsaid substrate to said bottom surface of said substrate, said additionalnon-conductive through via disposed on an opposite side of saidadditional conductive through via from said one or more interiornon-conductive through vias, said additional non-conductive through viacomprising a conductive core electrically insulated from said substrateby a dielectric liner and having a dielectric plug recessed between saidliner in an end proximate to said top surface of said substrate.
 14. Themethod of claim 13, further including: forming first and second exteriornon-conductive through vias extending from said top surface of saidsubstrate to said bottom surface of said substrate, said first andsecond exterior non-conductive through vias disposed different sides ofa core group consisting of said conductive through via, said one or moreinterior non-conductive through vias and said additional conductivethrough via, said first and second interior non-conductive through viaseach comprising a conductive core electrically insulated from saidsubstrate by a dielectric liner and having a dielectric plug recessedbetween said liner in an end proximate to said top surface of saidsubstrate.
 15. The signal transmission line of claim 8, furtherincluding: forming first and second additional conductive through wafervia extending from said top surface of said substrate to said bottomsurface of said substrate, sidewalls of said additional conductivethrough via in physical and electrical contact with said substrate,sidewalls of said first and second additional conductive through viaselectrically insulated from said substrate.
 16. The signal transmissionline of claim 15, further including: forming first one or more interiornon-conductive through vias extending from said top surface of saidsubstrate to said bottom surface of said substrate, said first one ormore non-conductive through vias intervening between said conductivethrough via and said first additional conductive through via, said firstone or more interior non-conductive through vias on an opposite side ofsaid conductive through via from said additional non-conductive throughvia, said first one or more non-conductive through via each comprising aconductive core electrically insulated from said substrate by adielectric liner and having a dielectric plug recessed between saidliner in an end proximate to said top surface of said substrate.
 17. Thesignal transmission line of claim 16, further including: forming secondone or more interior non-conductive through vias extending from said topsurface of said substrate to said bottom surface of said substrate, saidsecond one or more non-conductive through vias intervening between saidfirst additional conductive through via and said second additionalconductive through via, said second one or more interior non-conductivethrough vias on an opposite side of said conductive through via fromsaid non-conductive through via, said second one ore more non-conductivethrough vias each comprising a conductive core electrically insulatedfrom said substrate by a dielectric liner and having a dielectric plugrecessed between said liner in an end proximate to said top surface ofsaid substrate.
 18. The signal transmission line of claim 17, furtherincluding: forming an additional non-conductive through via extendingfrom said top surface of said substrate to said bottom surface of saidsubstrate, said additional non-conductive through via disposed on anopposite side of said second additional conductive through via from saidsecond one or more interior non-conductive through vias said additionalnon-conductive through via comprising a conductive core electricallyinsulated from said substrate by a dielectric liner and having adielectric plug recessed between said liner in an end proximate to saidtop surface of said substrate.
 19. The signal transmission line of claim18, further including: forming first and second exterior non-conductivethrough vias extending from said top surface of said substrate to saidbottom surface of said substrate, said first and second exteriornon-conductive through vias disposed different sides of a core groupconsisting of said conductive through via, said first one or moreinterior non-conductive through vias, said first additional conductivevia, said first one or more interior non-conductive through vias, andsaid additional conductive through via, said first and second exteriornon-conductive through vias each comprising a conductive coreelectrically insulated from said substrate by a dielectric liner andhaving a dielectric plug recessed between said liner in an end proximateto said top surface of said substrate.